Bacteria in the vagina during the estrous cycle in mares

Abstract: An understanding of the normal bacterial flora of any organ is essential to provide the background to conditions and interventions that might cause the flora to change. In the vagina of the mare, a change of bacterial flora could be induced by introduction of semen, treatment with antibiotics, backflow from an unhealthy uterus etc. Previous studies that have aimed to map the vaginal bacterial flora of the mare are not all conducted in the same way, and results are not altogether consistent. Therefore, this study was designed to provide a deeper understanding of the bacterial flora of the mare vagina, and possible changes throughout the estrous cycle. In total ten mares were included in the present study; the aim was to sample the cranial portion of the vagina of all ten mares on day 0 (ovulation), day 3, day 7 and day 14 of the estrous cycle. Seven mares were sampled according to plan, whereas three mares had some deviations in sampling days to fit their intended use as embryo recipients. The vaginal sampling was conducted with doubleguarded occluded swabs from the cranial floor of the vagina, in a similar manner to taking uterine samples. Ovulation was determined by rectal palpation and ultrasonic examination, and the day 0 samples were taken within ± 24 h of ovulation. Swabs were brought to the laboratory in Aime’s medium within 2-3 hours and were plated out immediately on agars. Results were registered as amount of growth (qualitatively), bacterial species and number of isolates. The results showed that bacterial growth was highest on day 3 and 7, representing the beginning and middle of diestrous. The dominant bacteria in the mare vagina in the present study were Escherichia coli and Streptococcus zooepidemicus. Fluctuations throughout the cycle were observed but these two bacteria were the most isolated on each of the sampling days. Escherichia coli was especially dominant in maiden mares, compared to the mares that had had foals. An increase in bacterial diversity throughout the estrous cycle was observed, being highest on day 14. These results suggest that there are changes in the bacterial flora of the mare vagina throughout the normal estrous cycle. Further research is required to confirm the results in other populations.